Should you avoid vitamin K-foods and cranberry juice while taking warfarin?

Vitamin K helps form blood clots in the body. This is important because blood clots prevent you from bleeding out when injured. Warfarin (the generic name for Coumadin®) is a medication that helps prevent blood clots from forming in excess and causing harm as in the case of stroke, pulmonary embolism or heart attack.

Eating inconsistent amounts of vitamin K can alter how warfarin works in your body. That said, it is imperative to eat a consistent amount of vitamin K every day. Inform your healthcare team of the foods you eat on a regular basis. This way, warfarin therapy can be tapered to your typical meal patterns.

Changing your current intake of vitamin K isn’t necessary while taking warfarin. Just be sure to meet the recommended amount of vitamin K each day. For adults, males aim for 120 micrograms and females 90 micrograms.

Vitamin K is found in a variety of foods (see below). Dark green vegetables tend to contain the highest amounts.

What is the role of cranberries with warfarin?Cranberries are often discussed in conjunction with warfarin therapy. Sometimes healthcare personnel, and even the medication’s own manufacturer, recommend avoiding cranberries and cranberry juice. Such statements likely stem from a 2003 United Kingdom’s Committee on Safety of Medicines alert to clinicians about unique cases of subjects undergoing warfarin therapy that had rare, negative reactions to the medication. However, the situations weren't typical. Patients consumed an abundance of cranberry juice (sometimes up to 8 ½ cups daily) and had underlying medical conditions.

Due to the Committee’s impact on healthcare provider’s recommendations against cranberries, studies have been conducted since. Two studies, one published in 2006 in the Journal of the American Dietetic Association and the other in 2009 in the Journal of Clinical Pharmacology, found no significant clinical interactions between warfarin and drinking 8-ounces of cranberry juice cocktail daily. Researchers concluded under appropriate monitoring by one’s healthcare team, cranberry juice is safe to drink in small amounts when taking warfarin.

Other foods may interact with warfarin...discuss your food choices with your healthcare provider!Other foods, herbs, supplements and alcohol have been shown to impact the effects of warfarin. These include everyday foods like garlic and ginger and supplements such as ginkgo, ginseng, coenzyme Q10 and Saint John’s wart. Due to this, always discuss food choices, alcohol intake and supplement practices with your pharmacist, registered dietitian and physician if prescribed warfarin (and any other medication for that matter!).

In the end, being on warfarin therapy won’t typically require an overhaul of favorite food choices. There is no need to discontinue enjoying dark leafy greens and cranberries on a regular basis. What is important are the frequency and quantity in which you eat vitamin K and cranberry-containing foods and keeping the lines of communication open between you and your healthcare team.